Challenging the CNS Targeting Potential of Systemically Administered Nanoemulsion Delivery Systems: a Case Study with Rapamycin-Containing Fish Oil Nanoemulsions in Mice.

Abstract

Despite extensive preclinical investigations, in-vivo properties and formulation characteristics that improve CNS drug delivery following systemic dosing of nanoemulsions remain incompletely understood. The CNS targeting potential of systemically administered nanoemulsions was evaluated by formulating rapamycin containing fish oil nanoemulsions, and testing the combined effect of formulation characteristics such as the circulation half-life and particle size distribution, on CNS delivery of rapamycin containing fish oil nanoemulsions in mice. Results generated with rapamycin nanoemulsions suggested that circulation half-life and particle size distribution did not impact the brain targeting efficiency of rapamycin containing fish oil nanoemulsions. Further, in the absence of any improvement in the systemic exposures of rapamycin, nanoemulsions did not outperform their aqueous counterpart with respect to the extent of CNS drug delivery. Our findings confirm that BBB penetration, which primarily depends on intrinsic drug-related properties, may not be significantly improved following encapsulation of drugs in nanoemulsions. Graphical Abstract The CNS targeting potential of systemically administered nanoemulsions was investigated by formulating various rapamycin containing fish oil nanoemulsions associated with different formulation characteristics such as the circulation half-life and particle size distribution. The targeting efficiency (TE) defined as the ratio of the brain exposures to the accompanying systemic exposures of rapamycin was estimated for each formulation following IV dosing in mice.